Measurement of Near-Field Electromagnetic Emissions and Characterization Based on Equivalent Dipole Model in Time-Domain

Abstract

In this paper, a method for representing electromagnetic emissions from a device under test (DUT) using an equivalent time dependent dipole array model deduced from the time-domain near-field scanned tangential magnetic fields is proposed. First, a 3D time-domain near-field scanning system is established to measure the tangential magnetic fields emitted from DUTs which are a transmission line above a ground plane and a printed circuit board (PCB) with several microstrips respectively. For time-domain measurements, two magnetic field probes are calibrated over a broad bandwidth for both amplitude and phase to obtain their complex probe factors. Then the measured magnetic fields are utilized to construct an equivalent time dependent dipole array model to represent the electromagnetic sources of the DUT. Parameters of the time dependent equivalent dipoles are directly calculated by fitting to the measured magnetic fields. The effects of different number of dipoles on the accuracy of the reconstructed magnetic fields from the PCB are studied. The reconstructed equivalent dipoles of the DUTs can be used to predict the electromagnetic fields at other observation levels. The results predicted by the equivalent dipole model are in agreement with the simulated and measured results. Index Terms-Equivalent dipole model, magnetic fields, printed circuit board, time-domain near-field scanning, transmission line.

Closed-Form Expressions of Electric and Magnetic Near-Fields for the Calibration of Near-Field Probes

“…Nevertheless, E and H fields decrease very rapidly with distance in near-field region so that they depend mainly on the charge and current distribution along the portion of the microstrip line placed just below the measurement point. E and H fields can be determined according to Gauss theorem (11) and Biot and Savart law (12) if this portion is electrically small. The evaluation of the length of this portion will be addressed later in part C, once closed-form expressions of E and H fields will be extracted.…”

“…If the line thickness is neglected, the tangential H-field at any point (xP,yP,r) can be determined by considering a uniform current density J flowing through a rectangular conductive sheet. If the current is oriented along x, the tangential H-field produced by the current distribution along the trace can be determined from the resolution of integral (12). According to ( 16) to ( 19), ( 12) is rewritten in (20).…”

“…Two typical methods propose to use waveguide (e.g. TEM cell) [11] and Helmholtz coils [12] (only for H-field probe) to generate a controlled homogeneous field. However, above PCB and IC, the fields are not homogeneous.…”

“…It is not straightforward due to the inhomogeneous medium. Most of the authors of technical publications about NFP calibration, such as [6]- [10] and [12]- [15], use 3D electromagnetic (EM) simulation. In spite of the great improvement of EM simulators these last years, it requires a solid expertise to select the A. Boyer, N. Nolhier, F. Caignet and S. Ben-Dhia are with LAAS, Univ.…”

Inter-Beam Co-Channel Downlink and Uplink Interference for 5G New Radio in mm-Wave Bands

“…In general, the interference analysis can be performed at any distance from the signal source antenna. In the case of a near-field, the influence between the individual elements of the multi-antenna system can be investigated [ 20 , 21 , 22 , 23 , 24 ]. In the case of a far-field, inter-beam [ 25 , 26 ], inter-cell [ 18 , 26 , 27 ], or inter-system interferences, i.e., the coexistence of different systems and networks [ 9 , 11 , 28 ], might be studied.…”